Recovery of by-products from distillation gases



Jan. 1, 1935. c. STILL 1,985,030

.RECOVERY OF BY-PRODUCTS FROM DISTILLATION GASES Filed Aug. 26, 1931 2 Sheets-Sheet l fig. la.

Jan. 1, 1935. c, sTlLL 1,986,080

RECOVERY OF BY-PRODUCTS FROM DISTILLATION GASES Filed Aug. 26, 1931 2 Sheets-Sheet 2 Patented Jan. 1, 1935 PATENT OFFICE RECOVERY OF BY-PRODUCTS FROM DIS- TILLATION GASES Carl Still, Recklinghausen, Germany Application August 26, 1931, Serial No. 559,574 In Germany August 30, 1930 1 Claim.

If ovens with external heatingffor the distillation of coal, viz. retort or chamber ovens for the production of gas and coke, are worked so that the volatile products of distillation are drawn off by suction from the interior of the mass of fuel, possibly at high suction pressures, by-products are obtained which are superior in quantity and value from those obtained in the usual methods of working. This relates more particularly to the hydrocarbons which can be condensed into the liquid state, viz. tar oils of lower and higher boiling points.

The object of the invention is to obtain the byproducts by the above-mentioned method of working so that their valuable properties can be fully utilized and their direct conversion can be partly efiected during the working process.

The accompanying drawings Figs.'1a and 1b taken together represent diagrammatically an example of the plant for carrying out the process according to the invention.

The reference 1 represents in vertical longi-- tudinal section a part of the chamber of a horizontal coke oven, which is closed by the door 2 and is charged with coal 3. There is the usual free gas collecting space 5 between the surface of the coal and the arch of the oven roof 4. The space 5 is connected to, but can be shut off from, a gas and tar main '7 by an ascension pipe 6. In the oven roof 4 a series of tubular members 8 is distributed over the whole length of the chamber; perforated tubes 9 are inserted from above into the members 8 with suitable packing and penetrate nearly to the bottom of the charge 3.

The members 8 project beyond the oven roof 4 and are connected by lateral tubes 10 with a gas collecting pipe 11 disposed along the chamber oven above the oven roof. The pipe 11 is connected over a valve with a second gas and tar main 12 extending over the whole oven battery. The pressure in the gas and tar mains 7 and 12 is maintained at a definite value by gas exhausters, described later, which draw oil the gases from the ovens, the pressure in the main 7 being very approximate to atmospheric, while in the main 12 there is usually a relatively high suction pressure which may amount, for example, to 200 mm. of the water gauge below atmospheric.

By the arrangements described two different kinds of distillation gases can be drawn off from the chamber 1, either simultaneously or in succe'ssion at different stages of distillation. For this purpose there is, usually in the gas collecting space 5, which is connected with the main 7, a gas pressure which is not notably different from that of the external atmosphere, but in the tubes 9 a relatively high suction pressure is usually maintained which can be varied as required during the whole duration of the working process by the insertion of suitable regulating devices between the the apparatus 14 through a pipe 15 and are led through an exhauster 16 to a further apparatus of any suitable kind for their after-treatment, with which this invention is not particularly concerned. The condensates of this ga's obtained by cooling in the apparatus 14, viz. the tar and ammonia liquor, are led away through pipes 17 and 18 and are further treated as described later.

The process according to the invention is mainly concerned with the distillation gases, collected in the main 12 and obtained by suction in the tubes 9 from the interior of the charge of coal 3. The first preliminary treatment of these gases, which is essential for the process, consists in cleansing the collecting pipes 11 and the main 12 and also the collecting space 8 in the roof 4, if it is suitably constructed, with an aqueous condensate in a warm condition deposited from the tar.

This cleansing is, as shown in the example illustrated in Fig. 1a of the drawings, preferably also extended to the other gas and tar main 7. For this purpose, the condensates collected in the two gas and tar mains '7 and 12, and which form a mixture of tar and ammonia liquor and are partly separated from the gases by air cooling and partly introduced by the cleansing, are led by pipes 19, 20,- 21 into a low lying separator 22. In the latter, the tar which sinks to the bottom is separated from the ammonia liquor which floats above. The tar it led from the bottom of the separator through a vertical pipe 23 into an adjacently disposed container 24 and from this is discharged from time to time. It represents a tar which contains a relatively high proportion in high boiling point substances of a pitch nature. The ammonia liquor floating in 22 is led through an overflow 25 into a second container 26. From the latter it is delivered by a pump 27 into an ascension pipe 28 which has branch pipe 31 provided for each oven and disposed parallel to the gas collecting pipe 11. The gas collecting pipe 11, with perhaps the collecting spaces 8, is supplied from the branch pipe 31 by a connecting pipe 32. The cleansing liquids or condensates which are led through and from the pipes and gas and tar mains are naturally warm owing to the sensible heat of the gases, so that it is possible by the described apparatus to effect the cleansing with an aqueous liquid which has a temperature of about 8085 C.

The cleansing of the gas collecting pipes and gas and tar mains is important as regards the quality of the withdrawn gas and also of the condensates obtained in the further course of the process, more particularly the tar oils. The higher temperature of the cleansing water is also useful for this purpose; it is also useful in keeping the paths, taken by the gases as they are I drawn by the tubes 9 from the interior of the coal 3, free from disturbing tar deposits, which would be formed by the use of cold cleansing liquid, and by offering resistance to the flow of the gases, would interfere with the maintenance of the suction pressure necessary for drawing off the gases from the interior of the coal. The distillation gases obtained by internal suction from the coal 3 and collected in the gas and tar main 12 are led thence through a pipe 33 to a cooling apparatus which, as shown in the drawings, consists of two water tube coolers 34, 35 coupled in series, but which might include a larger number of coolers of the same or other kind operating indirectly and arranged in series. The gas enters into the upper part of the cooler 35 from the first cooler 34 through the connecting pipe 36 and leaves the cooler 35 by a pipe 37. The cooling water is led in a path 38, 39, 40, as shown in Fig. 1a of the drawings, incounter-current to the gas. In this way, the individual coolers are maintained at temperatures decreasing in the direction of the flow of the gas and the gas is consequently cooled fractionally. By increasing the number of the coolers arranged in series, a further subdivision can be effected in correspondingly increased cooling or fractionating stages.

The gas is led through the pipe 37 from the last cooler 35 into an apparatus 41 acting as an impact separator which, for example, may be in the form of a tower provided with perforated diaphragms and filling materials such as loose rings resting thereon. The gas is drawn off from the apparatus 41 through pipes 42, 43 by a gas ex- .hauster 44. A condensate separator 45 is inserted directly behind the exhauster 44 in the path of the gas and contains, for example, an impact plate 46 and a collecting pot 4'7 at the bottom; the separator collects the condensate separated by centrifugal force from the gas in the exhauster 44 and also separates by impact the condensates which are carried along with the current of gas. For this latter purpose the apparatus 45 can preferably be replaced by a tar extractor of the usual construction operating on the impact principle, for example a Pelouse apparatus. A separate low lying container 48 or 49 is provided for each cooler 34 and 35, into which the condensates deposited in the individual coolers, viz. the tar oils and ammonia liquors, flow through pipes 50 or 51. A container 52 receives through a pipe 53 the tar oils separated from the gas in the separator 41. The tar oil condensate collected in the separator 45 is led into the container 52' by a pipe 54.

The containers 48 and 49 operate not only as collecting vessels, but also as means for separating the mixture of aqueous and oily particles flowing into them. The method of separation, in which the aqueous and oily particles lie in superimposed layers is indefinite, on account of the tar oils and according tothe conditions may be varied for the different containers. It may happen that either the oily particles or the aqueous particles sink; generally the latter is the case. In order to be able to remove at will the product required at the time from the containers that is, either the ammonia liquor or the tar oils, each container 48, 49 is provided with tapping positions 55, 56. The upper tapping positions 55 are connected with a horizontal collecting pipe 57 through three-way cocks 58 and the lower tapping points 56 are connected with a similar horizontal pipe 59 by threeway cocks 60. Vertical connecting pipes 61, in each of which there is a closing member, are provided between each two three-way cook 58 and 60 arranged vertically one over the other. At the right end of each of the horizontal branch pipes 57 and 59 there is a suction pump 62, 63 which delivers the drawn ofi liquids to apparatus described later.

The described arrangement of the apparatus 55 to 61 enables, as shown in Fig. 1a of the drawings, either the oily or aqueous constituents to be drawn oil from above or below by the pumps'62 or 63- from each of the containers 48 and 49. The details of the arrangement can be varied; for example, the three-way cocks 58, 60 can be replaced by valves or other closing devices independently operated at these positions. It is arranged that the pump 62 is always utilized for delivering the tar oils and the pumps 63 for the ammonia liquor. The further use of the liquids delivered by the pumps is described later.

The container 48 connected to the first gas cooler 34, viz. that operated at the highest temperature, receives by. the pipe 18 the tar and aqueous condensates drawn oil from the cooling apparatus 14 connected with the gas and tar main 7. The quantity of condensate deposited from this portion of gas is relatively small compared with that of the condensate separated from the portion of gas from the gas and-tar main 12; also, the properties of the tarry and also of the aqueous constituents of this condensate do not difier very much from those of the condensate obtained in the cooling apparatus 34 at the highest temperature, so that in order' to avoid complication of apparatus 'it is preferable to lead these condensates into the same container 48. l

A connecting pipe 64 is shown between the gas discharge pipe 13 from the main 7 and the gas discharge pipe from the main 12, and a similar pipe 65 between the gas discharge pipe 15 leading from the cooling apparatus 14 to the extractor 16 and the pipe 43 leading to the exhauster 44. In this case shutting-01f devices 66 must be inserted in the pipes 13 and 64 and shutting-01f devices 67 in the pipes 15 and 65, l

as shown in the drawings. The devices 66 and 67 must also be adapted to produce an adjustable throttling resistance for controlling the suction pressure. The connecting pipes 64 and 65 enable the gases collected in the gas and tar main 7 to be introduced either directly from this main or from the cooling apparatus 14, into the current of the distillation gases obtained by internal suction and withdrawn from the gas and tar main 12, and to treat them in common in the after processes. In either case the exhauster 16 is unnecessary or can be put out of action, since the exhauster 44 can then draw 01f al the distillation gases.

The further treatment of the gases drawn off F by the exhauster 44 into the separator 45 is as follows:

The gas first traverses two (or more) washing towers 68, 69 arranged in series and in which all the ammonia content is Washed with water.

thence through a pipe The second washing tower 69, from which the gas is withdrawn through the discharge pipe 70, is sprayed from a supply pipe '71 with fresh water. The weak ammonia liquor formed in the tower 69 is led away downwards through a discharge pipe '72 to the container 48 connected to the cooler 34, and mixes there with the ammonia liquor of similar property collected therein, and formed frbm the condensates from the coolers 34 and 14. The first washing tower 68 is sprayed with the weak ammonia liquor collectedin the container 48 through a supply pipe 73 and a pump '74. The suction pipe '75 of the pump '74 is connected to the container 48, so that according as the ammonia liquor therein forms the upper, or lower layer, it can be taken from an upper or lower tapping point 76 or '77 in the same manner as described previously for the pipes 5"! and 59. The strong am-' monia liquor formed in the washing tower 68 flows through a pipe '78 into a container 79. The similarly strong ammonia liquor, which has been collected in the container 49 connected to the last cooler 85 of lowest temperature (and possibly, if a larger number of gas coolers is provided, also ammonia liquor from a previous cooler or container) is led by the pump 63 into the container '79. The strong ammonia liquor collected in the container '79 is removed by a pump 80 and led to other positions (not shown in the drawings) for use or further treatment.

The gas led from the last ammonia washer 69 through the pipe 70 is now led to two (or more) washing towers 81, 82 (Fig. 11)) arranged in series which serve to wash by wash oil, the light oil content. In connection with the towers 81, 82 there are three low-lying containers 88,

'84, 85 for the wash oil to be circulated, by means of which the light oil is washed in counter-current in known manner as usual in the ordinary plants for obtaining benzol. The last container 85 contains, consequently,'all the fresh washing oil which is delivered by means of a pump 86 and an ascension pipe 87 to the top of the last washing tower 82. The washing .oil flows 88 into the container 84 and is delivered from the latter through a pipe 89 and an ascension pipe 90 to the top of the first washing tower 81. The saturated washing oil from the latter flows through a pipe 91 into the container 83 to be led thence to a purifying apparatus. This is efiected by means of a suction pipe 92 and pump 93 which delivers the saturated washing oil through an oil heater 94, indirectly heated by steam, into the stripping still 95. From the foot of the still 95 the hot washing oil flows through a pipe 96 into a cooling apparatus 9'7 constructed, for example, as a sprinkling cooler, in order to be cooled therein to the ordinary temperature, and returns in this condition through a discharge pipe 98 into the container 85 for fresh washingoil. A pipe 99 branched from the pipe 98 enables any portion of the cooled washing oil found in working to be superfluous, to be led into a container 100.

The light oil vapours forced into the still 95 with the aid of a steam jet are drawn through a pipe 101 into a cooler 102, the lower portion 103 of which forms a collecting and separating vessel; the light oils obtained are drawn off through a discharge pipe 104 into a container 105, and the water of condensation is removed through a pipe 106. A portion of the lowest boiling hydrocarbons of the gas treated,absorbed by the wash oil, remains on cooling uncondensed in the cooler 102 and leaves this vessel 103 as. a gas through an air escape pipe 128. In order to recover and to utilize these constituents, which represent hydrocarbons of high heating and lighting value, the pipe 128 is connected to the suction side of the exhauster 44, for example, by connection with the pipe 65, which is connected to the suction pipe 43 of the exhauster. V

The oily condensates which are obtained in the containers 48, 49 and 52, partly by the step by step cooling of the distillation gases obtained by internal suction from the coal, and partly by separation by impact and centrifugal action, have, in consequence of thetreatment by fractionization of the distillation gases, very different properties, more particularly in respect of their content both in light oils and also in higher boiling tar oils. On account of these differences, the method of obtaining the condensates in question by fractionization oifers advantages for their further treatment.

The oily condensate of the container 48 of the first cooling stage contains about up to 3 per cent.,

that of the second container of the last cooling stage up to 8 per cent, and that of the container 52 of the impact and centrifugal separator 20 to 25 per cent. of light oils, of which the principal portion consists of a small content in hydrocarbons of the benzine type, viz. the aliphatic type, and of a larger proportion of hydrocarbons of the benzol, viz. the aromatic type. Also, the character of the higher boiling tar oils is different. In the oily condensate of the container 48 there is relatively more of the higher boiling tar oils and a greater content in pitch constituents. The oily condensates of the containers 49 and 52, on the other hand, contain, apart from the light oils, mainly such tar oils and so little pitch constituents that after they are freed from the light oil constituents, they are well adapted as washing oils for washing the light oils in the washers 81 and 82. Consequently, in order to utilize this property, the oil collected in the container 52 may, for example, be delivered through a pump 107 and an ascension pipe 108 into an elevated container 109 from which it flows through a downfiow tube 110 into the container 83 for saturated washing oil of the apparatus for obtaining benzine.

This tar oil derived from the gas cooling, with its high content of benzine and benzol, and which is also very suitable to be used as the washing oil, is utilized in the process of obtaining the light oil by being led from there directly to the stripping still 95 and therein, together with the saturated washing oil circulating through the apparatus for obtaining the light oil, is freed of its content of light oil. The quantity of the introduced oil which remains after the treatment is used as-a washing oil in the process of obtaining the light oil. The excess quantity of oil introduced into the apparatus passes, as previously stated, finally into the container 100. In this way there is a continuous renewal of the washing oil used in the apparatus for obtaining the light oil by the fresh oil condensates obtained in the gas cooling. This additional tar oil condensate, utilized as a washing oil, can be derived either exclusively from the discharge 53 and 54 of the impact and centrifugal separators 41, 44, 45 or it can be taken as a tar oil condensate from the last cooling stage 85 of the gas cooling, which is discharged into the container 49, or, if there are additional stages in the gas cooling, the tar oil condensates can be taken from the previous lower cooling stages. In order to enable the condensates from the coolers to be used as washing oils, a pipe 112, branched from the delivery pipe 111 of the tar oil pump 62 and provided with a closing and regulating member, is connected to the container 52. By means of this device, the pump 62 can deliver tar oil from the container 49 (or from the previously disposed containers) into the container 52.

The tar oil condensate of the gas cooling in the container 48 of the first cooling stage 34 contains, as already stated, a considerable proportion of light oils, but is, however, otherwise not generally suited for a washing oil. In order to obtain this content of light oil before it leaves the apparatus as a by-product, the process is carried out in the following manner:

The tar oil of the container 48 is delivered by means of the pump 62 and the ascension pipe 111 into a separate elevated container 113. From the latter it flows through a downflow pipe 114 to a distilling and rectifying column 115 having at the lower portion a heating apparatus 116 and at the top a dephlegmator 117. The distillation is conducted so that all the products of which the highest boiling points are about 200-220C. pass through a delivery pipe 118. The distillation vapours are condensed in a cooler 119 and in that way a further quantity of light oil is obtained which passes through a discharge pipe 120 into a container 121. The residue in the column 115 is discharged by a pipe 122 and represents a tar of very high value, more particularly of low content in pitch.

'The removal of the content in light oil from the last cooling stages of the gas and from the impact and centrifugal separation, need not necessarily be conducted in the above described manner by means of the device of the apparatus for obtaining the light oil; instead of these, any other suitable apparatus for separation can be employed and in this way a purified oil can also be obtained that is adapted as a washing oil for obtaining the light oil. A construction for this modification of the process consists, for example, in the following:-

The rectifying column 115 is utilized atone time as previously described for separating out the tar oil condensate of the first gas cooling stage collected in the elevated container 118 and at another time for separating out the tar oil condensate of the last gas cooling stage collected in the elevated container 109. In order to enable this alternation to be made, there is a connecting pipe 123 between the downflow pipe from the container 109 and the downflow pipe 114 from the container 113. In this case, shutting-01f devices 124, 125 and 126 must also be provided in the three pipes 110, 114 and 123. By this arrangement of the pipes, the column can, as required, be supplied with tar oil from the container 109 or from the container 113. For this purpose it is only necessary that the containers 109 and 113 and the containers 48 and 49 supplying them should be made sufiiciently large so that the tar oil can be stored in one container system, while the other container system supplies tar oil for supplying the column 115. The column 115 must itself be sufficiently large and capable of a sufficient output to allow the treatment of both tar oils in the limited available time. 4

The last described modification of the process, in which the distillation column 115 is utilized alternately for the purifying of tar oils obtained from the earlier and later gas cooling stages, is employed with particular advantage in the case in which only the tar oil, containing the light oil and separated from the impact and centrifugal apparatus 41, 44, 45 and collected in the container 52, is treated in the stripping still 95 of the plant for obtaining the light oil. In this case, the tar oil of the earliest cooling stage is led from the container 48 to the column 115 alternately with the tar oil of the latest cooling stage from the container 49. This can be effected if, by the pump 62, with the connecting pipe 112 closed, oil from the container 48 and tar oil from the container 49 are delivered at different times through the pipe 111 into the container 113. Obviously, the container 113 must be completely emptied of the tar oil pumped into it and discharged through the pipe 114 into the column 115 before the other tar oil is pumped into it. In the treatment of the tar oil from the container 49 in the column 115, the residue of the distillation which is discharged through 112 collects and can, at will, be employed as a washing oil for obtaining the light oil. In the other case, in which the column treats the tar oil from the container 48, the residue of the distillation, as stated above, is removed as tar. In all cases, with whichever material to be distilled, the column 115 is supplied, the distillate which collects in the cooler 119 can be obtained as a light oil, in the same manner as the products of the apparatus for obtaining the light oil which collects in the cooler 102.

The washing of the ammonia, as described above, from the distillation gases to be treated, by the washing towers 68 and 69, is not essential to the process. Instead of this indirect method of obtaining ammonia, the so-called direct method can be used. In this case the ammonia washing towers 68 and'69 with their associated apparatus are entirely omitted and the gases discharged from the last light oil washer 82 through the pipe 127 are led to an ammonia saturator wherein their content of ammonia is fixed by sulphuric acid or other means.

What I claim is:

The process for the recovery of by-products' from distillation gases of difierent composition evolved in the charge of horizontal coke ovens which consists in drawing off distillate gases from ducts in the interior of the charge separately from the distillate gases collecting in the gas collecting space above the charge by applying a suction below atmospheric to said ducts and a pressure near atmmpheric to the gas collecting space above the charge, cooling the distillate gases from said ducts from high to low temperature indifferent cooling stages, separating the non-condensed tar oils of said gases by impact with solid bodies, collecting in a tank the tar oils from the cooling stages having the lowest temperature and those separated by impact, stripping the light oil content of the said tar oils in a stripping still and recirculating the stripped tar oil continuously in scrubbers for the recovery of light oil from the distillate gases, and continuously removing the surplus of stripped tar oil from circulation.

CARL STILL. 

